The following may be a subject invention developed under Department of Energy Contract DC-AC07-90ID13019, and the United States government may have certain rights and/or licenses in this invention.
1. Field of the Invention
The present invention relates to optical isolation circuits of the type used between signal processing and power control circuits having different electrical grounds. The invention is specifically designed for use in an electrically powered vehicle for coupling the vehicle control system with the power invertor/motor controller system.
2. Description of the Prior Art
Electric motors of the type used in the powertrain systems for electrically propelled vehicles utilize high voltage dc batteries for storing electrical energy. The dc power from the batteries is processed through a high voltage power invertor system that increases the voltage, conditions the waveform, and controls the application of voltage and current to the electric motors propelling the vehicle. The electrical invertor and motor control systems utilize high voltage and high current switching devices that create electromagnetic interference that, if uncontrolled, can cause substantial interference to the low power and low signal electronic systems used throughout the remainder of the electric vehicle.
It is therefore advantageous to isolate the power system used for propulsion from the electronic systems used in the remainder of the vehicle. One method of accomplishing this objective to electrically shield the battery and/or power control components, as well as providing separate grounds for the high voltage power conversion system components and for the low voltage signal control electronics.
The isolation between the two ground systems may be accomplished by using an optical isolator for converting the electrical control signals to optical energy, passing the optical signal across an electrical isolation bridge, and then using an optical receiving system for converting the optical signal back to an electrical control signal having a separate ground from the original transmitting system. While such optical isolators have been utilized in communications systems of the type employing frequency division multiplexing and time division multiplexing techniques, the prior art does not reflect the use of such optical isolators in a bi-directional digital network control system that is used between the electronic controller and the power propulsion systems of an electric vehicle.
It is therefore a first object of the present invention to provide an optical isolator interposed in a digital communications network for isolating the ground system used by the propulsion electronics from the ground system utilized by the signal control electronics. It is another object of the present invention that the optical isolator must have sufficient speed such that instantaneous, bit-wise contention among messages within the bi-directional digital communications network is not rendered inoperative and that the control speed of the system is not destabilized under worst case conditions. Still another object of the present invention is to provide an optical isolator with sufficient speed such that the timing between the opposite portions of the bi-directional digital communications network are not operatively disrupted.